Conductive layer of a large surface for distribution of power using capacitive power transfer

ABSTRACT

An apparatus ( 300 ) for supplying power to a load in a capacitive power transfer system comprises a power generator ( 350 ) operating at a first frequency; a transmitter comprising a plurality of first electrodes ( 310 ) connected to a first terminal of the power generator ( 350 ) and a plurality of second electrodes ( 320 ) connected to a second terminal of the power generator ( 350 ) of a transmitter portion of the apparatus ( 300 ); and a plurality of inductors ( 340 ), wherein each inductor of the plurality of inductors is connected between a pair of a first electrode and a second electrode of the plurality of first and second electrodes, wherein each inductor comprises, together with a parasitic capacitor ( 330 ) formed between each pair of the first electrode and the second electrode, a resonant circuit at the first frequency in order to compensate for current loss due to parasitic capacitances.

This application claims the benefit of U.S. provisional patentapplication No. 61/523,948 and U.S. provisional application No.61/523,964, both filed on Aug. 16, 2011, and U.S. provisionalapplication No. 61/671,855, filed Jul. 16, 2012.

The invention generally relates to capacitive power transfer and, moreparticularly, to parasitic capacitance when using large surfaces forpower distribution using capacitive power transfer.

A wireless power transfer refers to supplying electrical power withoutany wires or contacts, whereby the powering of electronic devices isperformed through a wireless medium. One popular application forcontactless powering is for charging portable electronic devices, e.g.,mobile phones, laptop computers, and the like.

One implementation of wireless power transfers is by an inductivepowering system. In such a system, the electromagnetic inductancebetween a power source (transmitter) and the device (receiver) allowsfor contactless power transfers. Both the transmitter and receiver arefitted with electrical coils, and when brought into physical proximity,an electrical signal flows from the transmitter to the receiver by agenerated magnetic field.

In inductive powering systems, the generated magnetic field isconcentrated within the coils. As a result, the power transfer to thereceiver pick-up field is very concentrated in space. This phenomenoncreates hot-spots in the system which limits the efficiency of thesystem. To improve the efficiency of the power transfer, a high qualityfactor for each coil is needed. To this end, the coil should becharacterized with an optimal ratio of an inductance to resistance, becomposed of materials with low resistance, and be fabricated using aLitze-wire process to reduce skin-effect. Moreover, the coils should bedesigned to meet complicated geometries to avoid Eddy-currents.Therefore, expensive coils are required for efficient inductive poweringsystems. A design for a contactless power transfer system for largeareas would necessitate many expensive coils, and thus for suchapplications an inductive powering system may not be feasible.

Capacitive coupling is another technique for transferring powerwirelessly. This technique is predominantly utilized in data transferand sensing applications. A car-radio antenna glued on the window with apick-up element inside the car is an example of a capacitive coupling.The capacitive coupling technique is also utilized for contactlesscharging of electronic devices. For such applications, the charging unit(implementing the capacitive coupling) operates at frequencies outsidethe inherent resonance frequency of the device. In the related art, acapacitive power transfer circuit that enables LED lighting is alsodiscussed. The circuit is based on an inductor in the power source(driver). As such, only a single receiver can be used and thetransmitter frequency should be tuned to transfer the maximum power. Inaddition, such a circuit requires pixelated electrodes which ensurepower transfer between the receiver and transmitter when they are notperfectly aligned. However, increasing the number of the pixelatedelectrodes increases the number of connections to the electrodes,thereby increasing the power losses. Thus, when having only a singlereceiver and limited size electrodes, the capacitive power transfercircuits discussed in the related art cannot supply power over a largearea, e.g., windows, walls, and so on. In addition, providing power overlarge surface areas poses several challenges. For example, a typicaluser would desire power from any arbitrary position over a large surfacearea. Moreover, when large surface areas are used for capacitive powertransfer there are various parasitic capacitances that impact theperformance of the system.

Therefore, it would be advantageous to provide a low cost and feasiblecapacitive power transfer system for wireless power applications overlarge surface areas, while reducing the impact of parasitic capacitanceappearing in such a capacitive power transfer system.

Certain embodiments disclosed herein include an apparatus for supplyingpower to a load of a capacitive power transfer system. The apparatuscomprises a power generator operating at a first frequency; atransmitter comprising a plurality of first electrodes connected to afirst terminal of the power generator and a plurality of secondelectrodes connected to a second terminal of the power generator of atransmitter portion of the apparatus; and a plurality of inductors,wherein each inductor of the plurality of inductors is connected betweena pair of a first electrode and a second electrode of the plurality offirst and second electrodes, wherein each inductor comprises togetherwith a parasitic capacitor formed between each pair of the firstelectrode and the second electrode a resonant circuit at the firstfrequency in order to compensate for current loss due to parasiticcapacitances.

Certain embodiments disclosed herein also include a circuit for reducingcommon mode (CM) currents in a capacitive power transfer system. Thecircuit comprises a first terminal connected to a first transmitterelectrode of the capacitive power transfer system, wherein the firsttransmitter electrode forms a first parasitic capacitor to a protectedearth connected to an earth ground; a second terminal connected to asecond transmitter electrode of the capacitive power transfer system,wherein the second transmitter electrode forms a second parasiticcapacitor to the PE; and wherein the circuit generates a first periodicvoltage signal between the first terminal and the earth ground, thecircuit further generates a second periodic voltage signal between thesecond terminal and the earth ground, wherein at least an amplitude ofeach of the first periodic voltage signal and the second periodicvoltage signal is controlled to essentially offset the common mode (CM)current flowing through the first parasitic capacitor and the secondparasitic capacitor.

The subject matter that is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features and advantages ofthe invention will be apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings.

FIG. 1 shows a capacitive power transfer system according to anembodiment;

FIG. 2 shows an electric diagram of the capacitive power transfer systemimplemented according to an embodiment;

FIG. 3 shows a schematic diagram of a capacitive power transmission gridwith parasitic capacity compensation, without a load;

FIG. 4 shows a schematic diagram of a capacitive power transmission gridwith parasitic capacity compensation, with a load;

FIG. 5 is a schematic diagram of a capacitive power transfer systemequipped with a current compensation circuit designed to eliminatecommon mode current paths according to one embodiment;

FIG. 6 is an electric diagram of a capacitive power transfer systemequipped with the current compensation circuit depicted in FIG. 5;

FIG. 7 is a timing diagram for controlling the switches of the currentcompensation circuit depicted in FIG. 5 according to one embodiment;

FIG. 8 is a wall covering having a backside covered with verticalconductive stripes with a bottom segment detailing electricalconnections thereto;

FIG. 9 is a wall covering having a backside covered with horizontalconductive stripes and vertical connecting lines;

FIG. 10 is a view of an electrical connection of a plurality of segmentswith integrated connections and connectors; and

FIG. 11 is a schematic drawing of a rectifier used in the power transfersystem of FIG. 5

FIGS. 12A, 12B, and 12C depict the operation of the current compensationcircuit according to various embodiments.

It is important to note that the embodiments disclosed herein are onlyexamples of the many advantageous uses of the innovative teachingsherein. In general, statements made in the specification of the presentapplication do not necessarily limit any of the various claimedinventions. Moreover, some statements may apply to some inventivefeatures but not to others. In general, unless otherwise indicated,singular elements may be in plural and vice versa with no loss ofgenerality. In the drawings, like numerals refer to like parts throughseveral views.

FIG. 1 shows an exemplary and non-limiting schematic diagram of acapacitive power system 100 utilized to describe various embodimentsdisclosed herein. The system 100 enables power transmissions over largeareas. The system 100 can be installed in places where open electricalcontacts are not preferred or are not desirable, such as bathrooms,retail-shops where regular variations are needed to illuminate aproduct(s), furniture, and the like. The system 100 can transfer powerover a large area, such that the system 100 can be utilized to powerdevices mounted on walls, windows, mirrors, floors, seats, aisles, andso on.

The system 100 includes a driver 110 connected to a pair of transmitterelectrodes 121 and 122 which are attached to an insulating layer 130.The system 100 also includes a pair of receiver electrodes 141 and 142connected to a load 150 and an inductor 160. Optionally, the system 100may include an inductor 112 coupled to the driver 110. The connectionbetween the transmitter electrodes 121,122 to the driver 110 is by meansof a galvanic contact or a capacitive in-coupling.

A power signal is supplied to the load 150 by placing the receiverelectrodes 141, 142 in proximity to the transmitter electrodes 121, 122without having a direct contact between the two. Thus, neither amechanical connector nor any electrical contact is required in order topower the load 150. The load 150 may be, but is not limited to, lightingelements (e.g., LED, LED string, a lamp, etc.), organic light emittingdiode (OLED) surfaces, displays, computers, power chargers,loudspeakers, and the like.

The driver 110 outputs an AC voltage signal having a frequency thatsubstantially matches the series-resonance frequency of a circuitconsisting of a series of the capacitors and inductors 112, 160. Thecapacitors—shown in dotted lines in FIG. 1 and labeled as C1 and C2—arethe capacitive impedance of the transmitter electrodes 121, 122 andreceiver electrodes 141,142. The impedances of the capacitors C1, C2 andinductor 160, and optionally inductor 112, cancel each other at theresonance frequency, resulting in a low-ohmic circuit. Thus, the system100 is capable of delivering power to the load 150 with very low powerlosses.

An electric diagram 200 of the system 100 is provided in FIG. 2. Themaximum power is obtained when the frequency of the power signal U_(gen)is close to the series-resonance of the circuit comprised of the loadR_(L), the resistor R_(S) (representing the inductor resistance)capacitors C₁ and C₂, and inductor L_(S). The series-resonance isdetermined by the values of the capacitors C₁, C₂ and inductor L_(S).The values of the capacitors C₁, C₂ and inductor L_(S) are selected suchthat they cancel each other at the operating frequency of the signalU_(gen). Therefore, only the series resistance of the inductor R_(S) andthe connectivity of the electrodes limit the power transfer. It shouldbe appreciated that this allows transferring AC signals characterized byhigh power with low frequency signals.

Referring back to FIG. 1, the driver 110 generates an AC signal of whichamplitude, frequency, and waveform can be controlled. The output signaltypically has an amplitude of tens of volts and a frequency of up to afew Mega Hertz (MHz). Frequency tuning between the generated signal andthe series-resonance is performed by changing the frequency, phase, orduty cycle of the signal output by the driver 110. Alternatively, thefrequency tuning is achieved by changing the capacitance or inductivevalues of the circuit connected to the driver 110.

The insulating layer 130 is a thin layer substrate material that can beof any insulating material, including for example, air, paper, wood,textile, glass, DI-water, and so on. Preferably, a material withdielectric permittivity is selected. The thickness of the insulatinglayer 130 is typically between 10 microns (e.g., a paint layer) and afew millimeters (e.g., a glass layer).

The transmitter electrodes 121, 122 are comprised of two separate bodiesof conductive material placed on one side of the insulating layer 130that is not adjacent to the receiver electrodes 141, 142. For example,as illustrated in FIG. 1, the transmitter electrodes 121, 122 are at thebottom of the insulating layer 130. In another embodiment, thetransmitter electrodes 121, 122 can be placed on opposite sides of theinsulating layer 130. The transmitter electrodes 121, 122 can be anyshape including, for example, a rectangle, a circle, a square, orcombinations thereof. The conductive material of each transmitterelectrode may be, for example, carbon, aluminum, indium tin oxide (ITO),organic material, such as Poly(3,4-ethylenedioxythiophene (PEDOT),copper, silver, conducting paint, or any conductive material.

The receiver electrodes 141, 142 can be of the same conductive materialas the transmitter electrodes 121, 122 or made of different conductivematerial. The total capacitance of the system 100 is formed by theoverlapping areas of respective transmitter and receiver electrodes 121,141, and 122, 142, as well as the thickness and material properties ofthe insulating layer 130. The capacitance of the system 100 isillustrated as C1 and C2 in FIG. 1. In order to allow electricalresonance, the system 100 should also include an inductive element. Thiselement may be in a form of one or more inductors that are part of thetransmitter electrodes or the receiver electrodes, distributed over thedriver 110 and the load (e.g., inductors 160 and 112 shown in FIG. 1),inductors incorporated within insulating layer 130, or any combinationthereof In an embodiment, an inductor utilized in the system 100 can bein a form of a lumped coil.

The load 150 allows for an AC bi-directional current flow. In anembodiment, the load 150 may include a diode or an AC/DC converter tolocally generate a DC voltage. The load 150 may further includeelectronics for controlling or programming various functions of the load150 based on a control signal generated by the driver 110. To this end,in an embodiment, the driver 110 generates a control signal that ismodulated on the AC power signal. For example, if the load 150 is a LEDlamp, a control signal output by the driver 110 may be utilized fordimming or color setting of the LED lamp.

The capacitive power system 100, as exemplary illustrated in FIG. 1,depicts a single load 150 that is powered by the driver 110. However, itshould be noted that the driver 110 can also power multiple loads, eachof which may be tuned to a different operational frequency.Alternatively, the multiple loads may be tuned to the same operationalfrequency.

FIG. 3 depicts an exemplary and non-limiting schematic diagram of acapacitive power transmission grid 300 with parasitic capacitancecompensation without a load. The construction of such exemplary andnon-limiting embodiments of capacitive power transmission grids isdiscussed with respect to FIGS. 8 through 10 herein below. In FIG. 3 thetransmitter portion is illustrated as comprising a power generator 350and a plurality of transmitter electrodes 310, 320 that form thetransmitter-side plates of the capacitors C₁ and C₂, respectively, asshown in FIG. 2. However, when the transmitter electrodes 310 and 320are large, then parasitic capacitance Cp 330 appears between thetransmitter electrodes 310 and 320. The transmitter electrodes 310 and320 are part of transmitter modules 301. This parasitic capacitance Cp330 impacts the performance of the capacitive power transfer system. Tocompensate for the parasitic capacitance Cp 330, an inductor Lc 340 isconnected in parallel to the transmitter electrodes 310 and 320. Thevalue for the inductor Lc 340 is selected such that it forms a parallelresonant circuit with the parasitic capacitance Cp 330, which is inresonance at the operating frequency of the power generator 350. As aresult, the current through the inductor 340 cancels out the capacitivecurrent of the parasitic capacitance Cp 330, such that the current isnegligible outside the transmitter module.

According to one embodiment, each transmitter module 301 comprises, forexample, two electrodes 310 and 320 and a compensating inductor 340,whereby the compensated transmitter module 301 does not cause additionalloading on the generator 350. A person of ordinary skill in the artreadily appreciates that this embodiment reduces the idle current thatwould otherwise be present in these kinds of capacitive power transfersystems. In a further embodiment the compensating inductor Lc 340 may bea variable inductor that can be adjusted to a necessary value tocompensate for a specific and unpredictable parasitic capacitance Cp330.

FIG. 4 shows an exemplary and non-limiting schematic diagram 400 of acapacitive power transmission grid with parasitic capacitancecompensation and a load. A receiver module 410 is capacitively coupledto the two electrodes (a transmitter module 301 of FIG. 3) of thecapacitive power transfer grid 300, as represented by the couplingcapacitors C₁ and C₂. Preferably, the receiver 410 comprises a matchinginductor (Lres) 411 that forms a series resonant circuit together withthe coupling capacitors C₁ and C₂, which is in resonance at an operatingfrequency of the power generator 350 of the capacitive power transfergrid 300. As noted above, in one embodiment the compensation inductorsLc 340 advantageously reduce idle currents of the power generator.

A capacitive power transfer system may also experience adverse effectsresulting from common mode (CM) currents induced between the alternatingcurrent (AC) potential of the electrodes of the transmitter portion andground, due to the parasitic capacitances of the transmitter electrodesto ground (as opposed to the parasitic capacitance between transmitterelectrodes discussed in detail hereinabove). While the below discussiondetails the parasitic capacitances of the transmitter electrodes toground, the discussion is also applicable for parasitic capacitances ofthe receiver electrodes to ground.

FIG. 5 shows an exemplary and non-limiting diagram of a capacitive powertransfer system 500 equipped with a current compensation circuit 560designed to eliminate CM current paths. Also illustrated in FIG. 5 areparasitic capacitances 542 and 544 of the transmitter electrodes toground from a physical perspective.

A power supply 510 is connected to a current compensation circuit 560,that together provide an opposite alternating voltage signal totransmitter electrodes 572 and 574. A pair of receiver electrodes 576and 578 is connected to a load 579, which is powered by the transmitterelectrodes 572, 574 by means of the capacitive coupling as discussedabove. Thus, between the transmitter electrodes 572, 574 and receiverelectrodes 576, 578 a pair of capacitors (not shown in FIG. 5) isformed.

Between each of the transmitter electrodes 572, 574 and earth ground 550there exists parasitic capacitors 542 and 544. Such parasiticcapacitance may occur from iron material in a concrete wall or ceiling,or could be the result of a conducting floor, or the like, forming aparasitic capacitance between two effective conductive plates that havea dielectric material therebetween.

Typically, the distance and the nature of the dielectric to ground isunpredictable, and hence so too is the specific capacitive value.Furthermore, the parasitic capacitances may be different for each of thetransmitter electrodes, i.e., if one transmitter electrode is situateddirectly above an enforcement iron rod in a wall and another transmitterelectrode is not. In addition, the shape of the transmitter electrodesmay be different, which also may lead to asymmetric parasiticcapacitances.

If an alternating voltage against earth ground 550 is applied to thetransmitter electrodes 572 and 574, currents flow through the parasiticcapacitors 542 and 544 as indicated in FIG. 5 and denoted by I_(p1) andI_(p2), respectively. These currents flow along the earth ground 550 andthen back as common mode (CM) currents (k_(CM)) through, for example, amains plug 511 of the power supply 510 back to the earth ground 550. Asa non-limiting example, the mains plug 511 may be a plug to a walloutlet to power supply 510. However, the CM currents may be a cause ofmalfunction, especially if the current in the connection cable isunwanted, and therefore must be limited according to electromagneticinterference (EMI) standards. Usually, bulky and expensive CM filterswith large inductors are applied to block the path for CM currents.However, it is difficult to match the filter components and a resultingfilter is big in size, prone to losses, and expensive.

According to various embodiments disclosed herein, the CM currents arereduced and essentially offset by means of the current compensationcircuit 560 as discussed herein below. The CM currents are offset to aminimal value, i.e., a value that an additional reduction of the CMcurrents cannot achieve, or is otherwise negligible. The currentcompensation circuit 560 includes two terminals (564 and 563) that areconnected to the transmitter electrodes 572 and 574 respectively. Tominimize the CM currents, the electrodes 572 and 574 are driven with avoltage asymmetrically to ground, such that the CM currents of thepositive electrode (e.g., electrode 572) and the negative electrode(e.g., electrode 574) essentially cancel each other, i.e., until acommon mode current flowing through the two electrodes is minimal, orotherwise negligible. With this aim, the AC voltage against the earthpotential of one of the terminals (564) is reduced. This also reducesthe related parasitic current I_(P1). The opposite voltage at theterminal (563) is increased such that the parasitic current I_(P2) hasthe same amplitude as I_(P1), whereby both currents compensate eachother. The common mode current I_(CM) is the sum of both parasiticcurrents I_(P1) and I_(P2). It should be noted the voltage differencebetween the two terminals 563, 564 remains the same for both operationmodes, thus the power transferred to the receiver electrodes is notaffected by the balancing of the common mode currents.

The operation for common mode current compensation is furtherillustrated in FIG. 12A. In the example shown in FIG. 12A, the powersupply generates sinusoidal voltage signals. The signals shown in FIG.12A are as follows:

U_(S1) represents the voltage signal between the first generatorterminal 564 and the earth ground 550. The amplitude of this voltagesignal (peak-to-peak) determines the amplitude of the first parasiticcurrent I_(P1). A DC offset is canceled by the parasitic capacitor.

U_(S2) represents the voltage signal between the second generatorterminal 563 and earth ground 550. The amplitude of this voltage signal(peak-to-peak) determines the amplitude of the second parasitic currentI_(P2). A DC offset is canceled by the parasitic capacitor.

I_(P1) represents the parasitic current through the capacitor C_(P1)(542) formed by the first electrode (572) to the earth ground 550. Dueto the capacitor C_(P1) (542), there is a phase shift to the voltageU_(S1).

I_(P2) represents the parasitic current through the capacitor C_(P2)(544) formed by the second electrode 574 to earth ground 550.

I_(CM) represents the sum of both parasitic currents I_(P1) and I_(P2),which is the resulting common mode current, and which is to becompensated.

U_(el) represents the voltage between the first terminal 564 and thesecond terminal 563. It is the difference of the voltages U_(S1) andU_(S2). The amplitude of U_(el) determines the amount of power that canbe transmitted in the capacitive power transmission system.

I_(el) represents the current through the transmitter electrodes (572,574) and the receiver electrodes (576, 578). The I_(el) current dependson the voltage U_(el) and the load 579 resistance.

The solid lines represent operation of a circuit according to the stateof the art (i.e., excluding the effect of the compensation circuit 560).As an example, the parasitic currents I_(P1) and I_(P2) are assumed tobe different in this operation mode because of asymmetries of theelectrodes. The dashed lines represent the operation according to theteachings disclosed herein. The AC voltage against earth potential ofone of the terminals (U_(S1)) is reduced. This also reduces the relatedparasitic current I_(P1). The opposite voltage U_(S2) is increased, suchthat the parasitic current I_(P2) has the same amplitude as I_(P1), sothat both currents compensate each other. As the graph representing thesignal U_(el) shows, the voltage difference between the two terminals(563, 564) remains the same for both operation modes. Therefore, thepower transmission is not affected by the balancing of the common modecurrents.

In one embodiment, the current compensation circuit 560 includes arectifier 561, the details of which are shown in FIG. 11, and aswitching bridge 562 consisting of four switches. By means of thecurrent compensation circuit 560 the transmitter electrodes 572, 574 aredriven with a voltage symmetrically to ground.

The operation of the current compensation circuit 560 will be describedwith reference to FIG. 6, where the switching bridge 562 is shown inFIG. 6 as switches 532, 534, 536, and 538. For ease of description thesame numerical references are used in FIGS. 5 and 6.

The power supply 510 is typically connected to a power grid, forexample, but without limitation, a main power grid to supply the powerto drive the power supply. The power supply 510 has a Phase lead,denoted P, and a neutral lead, denoted N. Usually, the N lead is alsoconnected to protected earth (PE). Via the rectifier 561, the groundpotential of the current compensation circuit is connected to the N leadand then also to PE.

The rectifier 561, as further shown in FIG. 11, comprises diodes 1111,1112, 1113 and 1114, as well as a capacitor 1115 connected at theoutput. The capacitor 1115 operates such that at low frequencies theleads P and N are free to alternate at the power signal frequency, whileat high frequencies, the capacitor 1115 operates as a short-circuit. Thehigh frequency is typically the frequency of the power supply signal.

Referring back to FIG. 6, via the switching bridge, the ground potentialof the transmitter electrodes (labeled as GND in FIG. 6) is connected tothe N lead and also to the PE. Thus, the earth ground 550 is at the sameelectrical potential as the transmitter ground GND. As noted above, ifan alternating voltage against GND is applied to the transmitterelectrodes 572, 574, currents (I_(p1) and I_(p2)) flow through theparasitic capacitors (capacitors 542 and 544 in FIG. 5). These currentsflow along earth ground and then back as common mode (CM) currentsthrough, for example, the mains plug 511, shown in FIG. 5, back to GNDof the transmitter circuit.

Using the current compensation circuit 560, the transmitter ground GNDis directly connected (e.g., via the rectifier 561) to the N lead duringa positive half-period of the voltage signal. Then, the DC-Supplyrectified voltage (Vdc) of the rectifier 561 is connected to the P leadof the power supply. During the negative half-period of the voltagesignal, this is reversed and the transmitter ground GND is connected tothe P lead, and Vdc is connected to the N lead. The transmitter groundGND and Vdc are connected by the rectifier's capacitor (e.g., capacitor1115 shown in FIG. 11). For high frequencies (e.g., the frequency of apower generator), this capacitor can effectively be considered a short,such that for high frequencies Vdc and GND are connected together(whereas for low frequencies and DC they are not). Since either Vdc orGND are directly connected to the N lead by a diode, for highfrequencies both are always connected to N (but only for highfrequencies).

It should be noted that the rectifier 561 may also include a powerfactor correction circuit (not shown). One of ordinary skill in the artwould readily realize that the rectifier 561 is merely used in anexemplary embodiment, and other rectifiers may be used, DC and AC,without departing from the scope of the invention. All such rectifiershave in common, a common mode current that may find a path through thepower supply back to a power generator. Therefore, the embodimentsdisclosed herein provide a solution for this common mode currentproblem.

In another embodiment, the current compensation circuit 560 may notinclude the rectifier 561. Such an embodiment can be utilized when a DCvoltage, for example, from a DC grid, can be supplied to the circuit560. It should be noted that even when DC voltage is supplied, CMcurrent can exist.

As noted above, the current compensation circuit provides a solution toreduce CM currents where the electrodes are driven with a voltagesymmetrically to ground. If the positive and negative electrodes areequal, their parasitic capacity to ground is also similar. Then, theinduced CM currents flowing through the parasitic capacitors of thepositive electrodes and the negative electrodes are equal in amplitudebut opposite in phase. Thus, they compensate each other and the overallCM current is zero.

The symmetric driving is achieved with a switching bridge 562 formed ofswitches 532, 534, 536 and 538 as shown in FIG. 6. In an embodiment, theswitching bridge 562 may be configured as a full bridge including twopairs of switches. For example, a first pair of switches may includeswitches 532 and 538, while a second pair of switches may includeswitches 534 and 536. In one embodiment, each pair of switches may becontrolled by the other pair of switches. The pairs of switches aredriven such that their output voltage is in opposite phase to each otheras shown in exemplary and non-limiting FIG. 7, in which solid lines 710and 720 correspond to U_(S1) and U_(S2), as shown in FIG. 6.

The output of the first pair of switches comprising switches 532 and 538is connected to the positive transmitter electrode, and the other outputof the second pair of switches including switches 534 and 536 isconnected to the negative transmitter electrode.

In most practical cases the parasitic capacitances in the vicinity ofthe positive and the negative transmitter electrodes (e.g., a wall towhich the electrodes 572, 574 are mechanically connected) are slightlydifferent. Thus, if the output voltage of the respective pairs ofswitches is exactly opposite, the currents through the parasiticcapacitors 542 and 544 may not compensate each other as expected, and aremaining CM current may flow. To account for such an asymmetry of theparasitic capacitances, the switching bridge of the current compensationcircuit is operated asymmetrically rather than symmetrically.

In one embodiment, the asymmetrical operation of the pair of switches isachieved by causing the duty cycle of the two pairs of switches to beunequal. This is shown in the exemplary and non-limiting FIG. 7 as adashed line output 730 that is slightly larger in duty cycle than theduty cycle of 710 (that in symmetric operation is equal to the dutycycle of 720). The duty cycle of the output voltage affects theamplitude of the fundamental frequency contribution to the pair ofswitches voltage against ground. By varying the duty cycle, thefundamental frequency amplitude can be adjusted such that the currentsthrough the parasitic capacitors are again equal and compensate eachother.

In order to avoid a phase shift between the positive and negativeparasitic current, the pulses of the first pair of switches and of thesecond pair of switches appear symmetrically in time. The center of thepositive pulse of the first pair of switches match exactly the center ofthe negative pulse of the second pair of switches (not shown). A commoncontrol method for the duty cycle of the full-bridge is a phase shiftcontrol between the two pairs of switches running at a 50% duty cycle,where a duty cycle control of each pair of switches is performed.

In another embodiment, the supply voltage for one of the two pairs ofswitches (or for both) is varied such that the voltage amplitude of thepair of switches is adjusted by varying the supply voltage. This can bedone by using a DC-to-DC converter. As a result, the duty cycles of bothpairs of switches can remain exactly equal (but opposite) such thathigher harmonic contributions of the CM currents may also becompensated.

FIGS. 12B and 12C illustrate the operation of the current compensationcircuit 560 that includes the switching bridge 562 consisting of fourswitches in a full-bridge configuration. FIG. 12B depicts the states ofthe signals U_(S1), U_(S2), I_(P1), I_(P2), I_(CM), U_(eI), I_(el), eachof which discussed above with respect to FIG. 12A. In addition, FIG. 12Bshows the states of the switches S_(1a) (534) S_(1b) (532), S_(2a)(538), and S_(2b) (536), in which a high signal indicates a closedswitch.

As noted, the voltage signals U_(S1) and U_(S2) at the terminals (564)and (563) have a pulse like shape. The parasitic currents I_(P1) andI_(P2) are represented by their fundamental frequency only, which issinusoidal and constitutes the most energetic part of the common modecurrent I_(CM).

The solid lines represent “normal” operation of a full-bridge withoutperforming the CM current compensation. The dashed lines represent thecommon mode currents compensation according to the embodiments disclosedherein. The I_(CM) is reduced and minimized by changing the amplitude ofthe power supply, which relates to the amplitudes of the pulses inU_(S1) and U_(S2). As a result, the amplitudes of the respectiveparasitic currents I_(P1) and I_(P2) are changed, such that theirrespective amplitudes compensate each other. As depicted by the graphI_(eI), the current I_(eI) flowing through the load is not beingaffected by the changes in the amplitudes of the parasitic currents. Itshould be noted that the current I_(eI) is also represented by itsfundamental frequency, which is valid, as the receiver is a resonantcircuit matched to the operating frequency of the power signal.

FIG. 12C depicts an embodiment current compensation circuit 560 thatincludes the switching bridge 562 consisting of four switches in afull-bridge configuration where the common mode currents are reduced bychanging the pulse widths of the signals U_(S1), U_(S2). The descriptionof signals depicted in FIG. 12C is similar to those illustrated in FIG.12B.

The solid lines represent “normal” operation of a full-bridge withoutperforming the current compensation. The dashed lines represent thecommon mode currents compensation according to the embodiments disclosedherein. The I_(CM) is reduced and minimized by modulating the width(thereby, the duty-cycle) of the power supply signal, which relates tothe amplitudes of the pulses in U_(S1) and U_(S2). As a result, theamplitudes of the respective parasitic currents I_(P1) and I_(P2) arechanged, such that their respective amplitudes compensate each other.Specifically, a wider pulse increases the amplitude of the fundamentalfrequency of the related parasitic current. Therefore, changing thepulse width can be used to adjust the parasitic currents until thesecompensate the common mode currents.

Several exemplary and non-limiting embodiments of capacitive powertransmission grids are discussed herein below. FIG. 8 shows an exemplaryand non-limiting wall covering having a backside covered with verticalconductive stripes with a bottom segment having details of electricalconnections thereto. As a non-limiting example a wall covering isdepicted as wallpaper 810 having a backside covered with verticalconductive stripes 820. The conductive stripes 820 are placed on theback side of the wallpaper material 810 that forms the insulating layer.When the wallpaper 810 is placed on a surface (not shown), for example,a wall, the conductive stripes 820 are between that surface and thewallpaper 810, while the wallpaper material 810 is in fact the insulatorlayer 130 discussed in greater detail with respect to FIG. 1hereinabove, where conductive stripes 820 form the transmitterelectrodes 122 and 124.

The conductive stripes 820 may be made of, for example, conducting ink,conducting paint, and the like. The stripes can be printed or added tothe backside of regular wallpaper, or they may be under an outer surfaceof the wallpaper 810. The connections to the driver 110 (FIG. 1) areprovided by interleaving the connections of the conductive stripes 820.That is, a first conductive stripe 820 is connected in the manner ofelectrode 121 (FIG. 1) and, therefore, to the supply line 834 of theconnection baseboard 830, while the immediately next conductive stripe820 is connected in the manner of electrode 122 (FIG. 1) and, therefore,to the supply line 832 of the conductive connection 830, and so on andso forth, alternating between the connections. The connections 832 and834 are part of a connection baseboard 830 designed to be operativewith, for example, the wallpaper 810 and accepting the output of driver110 (FIG. 1).

FIG. 9 shows an exemplary and non-limiting transmission grid of thecapacitive power system. The infrastructure is designed as a wallcovering having a backside covered with horizontal conductive stripesand vertical connecting lines. As a non-limiting example a wall coveringis depicted as wallpaper 900A and 900B in FIG. 9. Two sheets of suchwallpaper 900A and 900B are shown side-by-side. The electrodes 910 and920 begin with vertical connection lines that are directed horizontallyin opposite directions, so that they interleave with each otherresulting in a desired pattern allowing a horizontal-based wallpapersolution for capacitive power transfer. The structures shown in FIGS. 8and 9 are designed to allow for wallpaper that may be cut-to-measure, beconnected from the top or the bottom part of the wallpaper, and canoptionally share connections between neighboring conducting stripes ofneighboring wallpaper sheets. Moreover, the manufactured wallpaper maybe rolled into wallpaper rolls in any desired length.

It should be noted that power may be provided to the conducting stripesdirectly by clamping the wallpaper or protruding pins through the paperlayer. However, it is also possible to couple the power to theconducting stripes in a capacitive way. To this end, the transmitterelectrodes are positioned on the wallpaper. The power transmissionprinciple for injection of the power to the transmitter electrodes ofthe wallpaper may be, for example, the same principle as the way thepower is transferred from the wallpaper electrodes to the powerreceiver. The advantage of this configuration is that the position ofpower injection to the wallpaper can be freely chosen, and no damage isdone to the cover layer.

FIG. 10 shows an exemplary and non-limiting embodiment 1000 of anelectric connection of a plurality of segments with integratedconnections and connectors. A plurality of segments 1050A, 1050B, and1050C have integrated connection lines 1020 and 1030 that crossover atpoint 1040 without having an electrical connection at the intersectionpoint 1040. The connection lines 1020 and 1030 provide the power supplyconnectivity to the segments. The wire 1020 is electrically connected tothe segment 1050A. When two segments are mounted adjacent to each other,their corresponding segments are connected to different electricalconnection lines.

For example, in FIG. 10, the center segment 1050B of 1010B is connectedin fact to a different connection line (i.e., connection line 1030) thanthe segments 1050A and 1050C (i.e., connection line 1020). As a result,the segments alternate in polarity, thereby providing the differentelectrodes as discussed in more detail with respect of FIG. 1hereinabove. It should, therefore, be understood that the segment 1050Aoperates, for example, as electrode 121 shown in FIG. 1, while segment1050B operates as electrode 122 shown in FIG. 1.

While the present invention has been described at some length and withsome particularity with respect to the several described embodiments, itis not intended that it should be limited to any such particulars orembodiments or any particular embodiment, but it is to be construed withreferences to the appended claims so as to provide the broadest possibleinterpretation of such claims in view of the prior art and, therefore,to effectively encompass the intended scope of the invention.Furthermore, the foregoing describes the invention in terms ofembodiments foreseen by the inventor for which an enabling descriptionwas available, notwithstanding that insubstantial modifications of theinvention, not presently foreseen, may nonetheless represent equivalentsthereto.

1. An apparatus for supplying power to a load in a capacitive powertransfer systems configured wirelessly distribute power over a largesurface, comprising: a power generator operating at a first frequency; atransmitter comprising a plurality of first electrodes connected to afirst terminal of the power generator and a plurality of secondelectrodes connected to a second terminal of the power generator of atransmitter portion of the capacitive power transfer system, wherein theplurality of first electrodes and the plurality of first electrodes andthe plurality of second electrodes are mounted on the large surface; anda plurality of inductors, wherein each inductor of the plurality ofinductors is connected in parallel between a pair of a first electrodeand a second electrode of the plurality of first and second electrodes,wherein each inductor comprises, together with a parasitic capacitorformed between each pair of the first electrode and the secondelectrode, a resonant circuit at the first frequency in order tocompensate for current loss due to parasitic capacitances.
 2. Theapparatus of claim 1, wherein each inductor of the plurality ofinductors is a variable inductor.
 3. A method for reducing idle currentsin a transmitter for supplying a power to a load connected in acapacitive power transfer system configured to distribute power overlarge surface, comprising: operating a power generator at a firstfrequency having a first terminal and a second terminal; connecting afirst electrode, of a transmitter portion of the capacitive powertransfer system to the first terminal of the power generator; connectinga second electrode of the transmitter portion of the capacitive powertransfer system to the second terminal of the power generator; andconnecting an inductor in parallel between the first electrode and thesecond electrode, the inductor having an inductance to create a resonantcircuit with a parasitic capacitor formed between the first electrodeand the second electrode, such that the resonant circuit resonates atthe first frequency.
 4. The method of claim 3, wherein the inductor is avariable inductor.
 5. The method of claim 4, further comprising:adjusting variable inductance of the variable inductor to cause theresonant circuit to resonate at the first frequency.
 6. A circuit forreducing common mode (CM) currents in a capacitive power transfer systemconfigured to wirelessly distribute power over a large surface,comprising: a first terminal connected to a first transmitter electrodeof the capacitive power transfer system, wherein the first transmitterelectrode forms a first parasitic capacitor to a protected earthconnected to an earth ground; and a second terminal connected to asecond transmitter electrode of the capacitive power transfer system,wherein the second transmitter electrode forms a second parasiticcapacitor to the protected earth; wherein the circuit generates a firstperiodic voltage signal between the first terminal and the earth ground,the circuit further generates a second periodic voltage signal betweenthe second terminal and the earth ground, wherein at least an amplitudeof each of the first periodic voltage signal and the second periodicvoltage signal is controlled to essentially offset the common mode (CM)current flowing through the first parasitic capacitor and the secondparasitic capacitor.
 7. The circuit of claim 5, wherein the firstperiodic voltage signal consists of a first period of time and a secondperiod of time, wherein during the first period of time a voltage levelof the first periodic voltage signal is substantially positive, andduring the second time period a voltage level of the first periodicvoltage signal is substantially negative; wherein the second periodicvoltage signal consists of a first period of time and a second period oftime, wherein during the first period of time a voltage level of thesecond periodic voltage signal is substantially negative, and during thesecond time period the voltage level of the second periodic voltagesignal is substantially positive.
 8. The circuit of claim 7, whereineach of the first and second time periods of the first periodic voltagesignal substantially matches each of the first and second time periodsof the second periodic voltage signal respectively.
 9. The circuit ofclaim 8, wherein parasitic capacitances in a vicinity of the first andsecond transmitter electrodes are different, wherein the vicinity of thefirst transfer electrode and the second transmitter electrode includesat least a surface to which the first transmitter electrode and secondtransmitter electrode are mechanically connected.
 10. The circuit ofclaim 6, wherein the circuit is further configured to change a width ofeach of the first periodic voltage signal and the second periodicvoltage signal until the CM current flowing through the first parasiticcapacitor and the second parasitic capacitor is essentially offset. 11.The circuit of claim 10, further comprising: a switching bridgeincluding a first pair of switches and a second pair of switches;wherein the first pair of switches includes two switches, a switch isconnected to the first transmitter electrode and a first terminal of apower supply generator and a second switch is connected to the secondtransmitter electrode and a second terminal of the power supplygenerator; wherein the second pair of switches includes two switches, aswitch is connected to the first transmitter electrode and the secondterminal of the power supply generator and a switch is connected to thesecond transmitter electrode and to the second terminal of the powersupply generator, the second terminal of the power supply generator isconnected to the protected earth for connection to the earth ground; andwherein switching of each of the first pair of switches and the secondpair of switches is controlled to essentially offset the CM currentflowing through the first parasitic capacitor and the second parasiticcapacitor.
 12. The circuit of claim 11, wherein the CM current is a sumof the currents flowing through the first parasitic capacitor and thesecond parasitic capacitor.
 13. The circuit of claim 11, wherein theswitching of each of the first pair of switches and the second pair ofswitches is controlled to change amplitudes of currents flowing throughthe first parasitic capacitor and the second parasitic capacitor untilthe amplitudes of the currents essentially cancel each other.
 14. Thecircuit of claim 11, wherein the switching of the first pair of switchesis controlled to change a width of a voltage pulse between the secondtransmitter electrode and the earth ground, wherein the switching of thesecond pair of switches is controlled to change a width of a voltagepulse between the first transmitter electrode and the earth ground. 15.The circuit of claim 11, wherein the first pair of switches and thesecond pair of switches are controlled in an asymmetric operation,wherein the asymmetric operation comprises a different duty cycle forcontrol of the switches of the first pair of switches and control of theswitches of the second pair of switches.